This invention concerns axial flow rotary crop material separators and their rotors and particularly the arrangement of crop material engaging elements on such rotors.
Although the term "separating" is properly applied only to "the isolating of detached seed, small debris and unthreshed material from the bulk", the term "separator" is sometimes used rather broadly to cover a crop processing arrangement providing, for example, the functions of receiving or infeeding, threshing, separating, and discharge of straw. "Separator" is sometimes used in this sense in the following.
The general operation of axial flow separators is well known. Typically, a separator housing, including at least one grate portion, surrounds a rotor so as to define an elongated annular space. A feeding arrangement introduces crop material to the upstream end of the annular space. The housing and/or rotor carry crop-engaging elements for displacing the crop material in a downstream direction so that as the rotor rotates, rotor and housing cooperate to propel crop material downstream in a generally spiral path, through threshing and separating stages. Grain and other small fractions leave the housing by passing outward through the grate but most of the straw remains to be discharged from the housing at its downstream end.
The field capacity of combine harvesters using axial flow rotary separators has often been limited by the material handling characteristics of their separators. Especially difficult is the handling of long tough rice straw, particularly in the threshing section. Further, a particular problem inherent in all known arrangements of crop material engaging elements on a rotor is the tendency to "roping" in certain types and conditions of crop material. Tight rolls or ropes of crop material, possibly up to 150 millimeters diameter and 1500 millimeters long, are formed ahead of the crop material-engaging elements of the rotor, in the space between rotor and housing. Typically, ropes form with their axes at any given point approximately perpendicular to the direction of the spiral path in which the crop material is being propelled relative to the housing at that point. No known arrangements of rotor crop-engaging elements have any specific anti-roping characteristic and, in fact, many rotors encourage roping by carrying elements which present quite extensive and continuous surfaces having an orientation not far removed from that of a perpendicular to the "spiral" direction of crop material movement at any particular point. This applies particularly to longer or uninterrupted threshing bars having a helical configuration chosen to contribute directly to axial indexing or downstream conveying of the crop material. Rotor elements offering continuous walls or surfaces of substantial axial extent athwart the spiral path in which material is being propelled provide a wall against which material may be rolled and rope formation may begin. Even though "slippage" occurs (the mean circumferential speed of the crop material mat is less than that of the rotor periphery) incipient ropes are acted upon by successive similarly oriented rotor element surfaces until the rope is of such dimensions as to seriously affect separator performance--grain kernels become entrained in the rope and lost with the straw discharge; the forced slippage of rotor elements over heavy ropes causes high stresses in housing and rotor elements, noisy operation and excessive power consumption; and the roping tendency makes the separator much less tolerant of uneven feeding from the cutting platform or other gatherer of the combine.
Attempts to reduce the roping problem, particularly in rice harvesting in both conventional (circumferential flow at the threshing cylinder) and axial flow threshing sections, have included the use of spike-tooth rotors. However, the spike teeth have been arranged only in axially extending rows or arrays so that collectively, especially if fairly closely spaced axially, they may still present an effective "wall" oriented so as to encourage rope formation especially when used in conjunction with conventional bar-type concaves.